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Note: All the posts are based on practical approach avoiding lengthy theory. All have been tested on some development servers. Please don’t test any post on production servers until you are sure.

Monday, December 06, 2010

Voting Disk and OCR Files Backup (Win 10gR2)

Voting Disk:

The voting disk is nothing but a file that contains and manages information of all the node memberships. Oracle RAC uses the voting disk to determine which instances are members of a cluster. The voting disk must reside on shared disk. For high availability, Oracle recommends that you have multiple voting disks. The Oracle Clusterware enables multiple voting disks but you must have an odd number of voting disks, such as three, five, and so on. If you define a single voting disk, then you should use external mirroring to provide redundancy.

I've windows environment for my RAC so I will not be using dd instead I'll use Oracle supplied utility ocopy

There some changes in the way we handle now the important Clusterware components Voting Disk and Oracle Cluster Registry (OCR): Amazingly, we can now store the two inside of an Automatic Storage Management (ASM) Disk Group, which was not possible in 10g.

The Voting Disk (or Voting File, as it is now also referred to) is not striped but put as a whole on ASM Disks – if we use a redundancy of normal on
the Diskgroup, 3 Voting Files are placed, each on one ASM Disk. This is a
concern, if our ASM Diskgroups consist of only 2 ASM Disks! Therefore,
the new quorum failgroup clause was introduced:

The failgroup fg3 above needs only one small Disk (300 MB should be
on the safe side here, since the Voting File is only about 280 MB in
size) to keep one Mirror of the Voting File. fg1 and fg2 will contain
each one Voting File and all the other stripes of the Database Area as
well, but fg3 will only get that one Voting File.

Another important change regarding the Voting File is that it is no longer supported to take a manual backup of it with dd or ocopy. Instead, the Voting File gets backed up automatically into the OCR

OCR

OCR is a file that manages the cluster and RAC configuration. OCR contains information pertaining to instance-to-node mapping, node list and resource profiles for customized applications in your Clusterware.

Oracle Clusterware automatically creates OCR backups every four hours and it always retains the last three backup copies of the OCR. The CRSD process that creates the backups also creates and retains an OCR backup for each full day and then at the end of a week a complete backup for the week. So there is a robust backup taking place in the background. And you guessed it right; you cannot alter the backup frequencies. This is meant to protect you, the DBA, so that you can copy these generated backup files at least once daily to a different device from where the primary OCR resides. These files are located at %CRS_home/cdata/my_cluster.

The OLRIn Oracle Clusterware 11g Release 2 an additional component related
to the OCR called the Oracle Local Registry (OLR) is installed on each
node in the cluster. The OLR is a local registry for node specific
resources and is used by cluster and non-cluster Oracle processes. One
use of the OLR is to store the location of the of the voting disk. This
information is used when the node is being started and attempts to join
the cluster. The OLR file is located in the
grid_home/cdata/.olr .
You can view the status of the OLR file on each node by using the ocrcheck command with the –local parameter as seen here:
D:\app\11.2.0.3\grid\BIN>Ocrcheck -local -configOracle Local Registry configuration is : Device/File Name : D:\app\11.2.0.3\grid\cdata\or-11.olr You can also use the ocrdump to see the contents

D:\app\11.2.0.3\grid\BIN>Ocrdump -local -stdout
Note: Oracle
Clusterware can access the OCR and the voting disks present in ASM even
if the ASM instance is down. As a result CSS can continue to maintain
the Oracle cluster even if the ASM instance has failed.